The present invention relates to the art of earth boring and more particularly to an improved bearing system for a rotary rock bit.
A rotary rock bit is adapted to be connected as the lower member of a rotary drill string. As the drill string is rotated, the bit contacts and disintegrates the formations to form an earth borehole. The rotary rock bit includes at least one bearing pin that extends angularly downward from the main body of the bit. A cone cutter is mounted upon the bearing pin and adapted to rotate thereon. Individual bearing systems promote rotation of the cone cutter. These bearing systems have traditionally been roller bearings, ball bearings, friction bearings, or a combination of the aforementioned bearings. The cone cutters include cutting structure on their outer surfaces that serves to disintegrate the formation as the bit is rotated.
In addition to the rotational forces, the bit is subjected to a thrust load during operation. The weight of the drill string and the downward force applied by the rotary drill equipment apply a substantial thrust load upon the rotary rock bit. The thrust load is divided into an out thrust component substantially parallel to the axis of cutter rotation and a radial thrust component substantially perpendicular to the axis of cutter rotation.
In prior art earth boring bits, the out thrust component is taken primarily by a thrust button in the nose of the cone cutter that rotates against a hard face surface on the end of the bearing pin and a thrust flange surface on the inner surface of the cone that rotates against a thrust flange surface on the bearing pin, and secondarily by the ball bearing system. Prior art rotary bits have experienced early failure because of their inability to support the extensive thrust loading. The ball raceways and ball bearings have not been sufficient to effectively carry the out thrust component of the thrust load. The size of the ball bearings was limited by the space available in the cutter shell and on the bearing pin. The use of friction bearings to carry the out thrust load increased the manufacturing costs and resulted in the generation of heat in the bearing area.